In the state of the art, some thermoplastic elastomer (TPE) variants are to be found, which are used for adhesion to cross-linked diene rubber, especially EPDM. These are, on the one hand, TPEs based on EPDM/polypropylene (PP) and, on the other hand, TPEs based on styrene block copolymers (SBC). Both types are known and are used in different applications. A preferred use of the variants is adhesion to cross-linked EPDM. Cross-linked EPDM is used for example as seal running around the area of the window pane on motor vehicle side doors. For technical production reasons the seal used for this is not already produced as a ring-shaped band, but as an interrupted band. However, in order that the seal running around along the window pane of a motor vehicle door is tight, both ends of the band must be tightly connected to each other. Until now this has frequently been achieved with one of the named TPEs. It is however known in the case of both the named TPE variants that they have both advantages and disadvantages.
Furthermore, it is also possible to vulcanize rubber onto rubber. For example, for this, the seal consisting of cross-linked EPDM is tightly connected at both ends with EPDM instead of TPE. In other words, EPDM is vulcanized onto the seal. This method has the disadvantage of long cycle times in comparison with the method with the TPE variants.
The TPEs used until now thus already exhibit a bleeding-out of plasticizers after a short period of weathering or irradiation with UV light. This bleeding-out, also alternatively called oiling-out, leads to unsightly black streaks on the paintwork due to leaked-out constituents washed down with rainwater, particularly in the case of light-coloured motor vehicles.
The TPE variant EPDM/PP furthermore has the disadvantage of only achieving good adhesion results on cross-linked EPDM at very high temperatures greater than 270° C. The process is therefore very energy-intensive, and at the same time the cooling time required and thus the cycle time are increased due to the high processing temperature.
The TPE variant based on SBC, with good adhesion, has the disadvantage of being sticky vis-à-vis glass or exhibiting a high degree of friction vis-à-vis glass. When used in motor vehicle window pane seals, this can become a disadvantage as there is a direct contact with the glass pane and the pane also moves over the TPE. The friction is increased by weathering and UV exposure which the motor vehicle experiences due to natural, external influences; the SBC material slowly becomes sticky. In order to achieve a sufficient adhesion to EPDM, low-molecular-weight (sticky) SBCs are used, which have the disadvantage that, in the course of time, they migrate onto the surface. It has been shown that, in the course of time, the friction vis-à-vis glass is further increased.